1. Field of the Invention
The present invention relates to a design for a sense amplifier used in a memory circuit. In particular, the present invention relates to a design for sense amplifiers used in a memory circuit, such as a flash memory circuit.
2. Discussion of the Related Art
In a memory circuit, e.g., a non-volatile floating gate memory circuit (“flash” memory circuit), a sense amplifier circuit is shared by numerous memory cells for sensing their stored logic values. Typically, to sense the logic value stored in a memory cell, the output terminal of the memory cell is selectively coupled to an input terminal of the sense amplifier circuit, which amplifies the voltage received at the input terminal to provide a logic signal output that represents the stored logic value. This output logic signal is typically stored into a latch circuit external to the sense amplifier circuit. Typically, because a memory cell represents the logic value stored by the presence or the absence of a small amount of electrical charge, the memory circuit has little drive capability. Consequently, the sense amplifier circuit is required to have a high gain to allow it to amplify the signal provided by this small amount of electric charge into an output signal of conventional signal levels that can be processed in a conventional logic circuit. To achieve high performance, the output signal is required to settle rapidly. More recently, sense amplifier circuits are also designed with low power dissipation as a design goal. Thus, numerous design challenges are presented by a sense amplifier circuit.